Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to a battery pack. The internal combustion engine in a series hybrid is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by also operating in a generator mode to recharge the battery pack. Parallel hybrid architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the preferable gear ratios for wide range operation.
One hybrid powertrain architecture comprises a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving power from a prime mover power source and an output member for delivering power from the transmission, typically to a vehicle driveline. First and second motor/generators are operatively connected to an energy storage device for interchanging electrical power between the storage device and the first and second motor/generators. A control unit is provided for regulating the electrical power interchange between the energy storage device and the first and second motor/generators. The control unit also regulates electrical power interchange between the first and second motor/generators.
Engineers implementing hybrid powertrain systems attempt to meet fuel economy and emissions targets by determining engine power from a required road-load power plus an additional quantity of engine power based on the energy storage system's (e.g. battery's) state-of-charge. Following determination of engine power, the engine's optimal fuel economy or optimal emissions map, or a combination thereof, may be used to select the engine's torque/speed operating point. The battery power used by the system is that which is required, in combination with the engine power, to meet the road-load power requirements and to compensate for power losses within the system.
Some known systems do not simultaneously optimize power flow from all the propulsion system components. Typically, only engine operation is optimized. Additional factors such as system mechanical and electrical losses and battery usage factors are often not used in selecting the overall system's preferred operating point. Systems which attempt to account for system mechanical and electrical losses and battery usage factors in optimizing power flow of all propulsion system components have faced a daunting task of simultaneously calculating the various power flows, consuming substantial amounts of on-board computer processing resources, both in terms of processing time and throughput, and algorithm complexity.
Therefore, there is a need to develop a hybrid powertrain control system which can optimize power flow from all the propulsion system components, accounting for losses, in a manner which effectively uses on-board computing resources.